This invention relates to direction drilling of bores, particularly (though not exclusively) to produce fluid such as oil or gas from an underground formation.
When drilling a borehole to extract oil or gas from an under-ground formation, it is often desirable to drill the borehole so that it includes one or more bends or curves. For example, it nay be necessary to avoid an existing well, or to aim for the reservoir to be exploited. Similarly, in drilling a borehole to take piping and/or cables beneath a road or river, it is necessary to guide the course of the borehole.
Wells are drilled using a drill string which consists of a drill pipe with a bottom hole assembly at its bottom end. Traditionally, the drill string has been rotated. With such a string, directional control is achieved by providing a collar around the bottom hole assembly which can be locked to the sides of the bore. The collar has a hole through which the main rotating body of the bottom hole assembly passes. This hole is offset to skew the body of the bottom hole assembly and so cause the bore to deviate from straightness.
More recently, drill strings using coiled tubing have become popular. With this, the drill string is non-rotating, and carries a motor at the bottom of the bottom hole assembly. The motor is driven either by the fluid pumped down the drill string or electrically. (Fluid flow through the drill string is required to wash away the debris resulting from the drilling and to lubricate the system.)
With a coiled tubing drill string, the bottom hole assembly can include a bent sub having nose tubing which carries the motor at its end. The drilling thus automatically tends to deviate from straightness. The bottom hole assembly also includes an orienter, which can be operated to turn the bent sub to control the bearing (as seen looking along the bottom hole assembly) of the deviation of the drilling. GB 2 271 791 A (Camco/Pringle) is in essence an example of this.
The use of a bent sub results in the drilling deviating continuously. Typically, however, it will be desired to drill a borehole which is curved along only a part or parts of its length, with the remainder being straight. There are two techniques for achieving this with the use of a bent sub.
One is to include the bent sub in the bottom hole assembly only for those portions of the bore where deviation is desired; at the beginning and end of each such portion, the directional drilling assembly is removed from the borehole, the bent sub removed or attached, and the drill string re-introduced to the bore hole. Having to interchange straight and directional drilling assemblies adds to the time and cost of a drilling operation.
The second technique is to rotate the orienter continuously in order to produce a nearly straight borehole. This is an inefficient and inaccurate way of producing a straight-pathed borehole. Further, rotating the orienter to simulate straight drilling, or to change or control the azimuthal angle of the directional drilling assembly, is made difficult due to friction between the drill string below the angled portion of the bent sub and the walls of the borehole, or the walls may completely block such rotation. It will be seen that this depends oil the length of the drill string below the angled portion of the bent sub, the angle of the bent sub, the diameters of the borehole and the drill assembly, and the path of the borehole.
Another difficulty associated with such a directional drilling assembly is that the rotation of the directional drilling assembly""s drill bit exerts a torsional force upon the bent sub and orienter, acting to change the azimuthal angle of the bent sub. As the drill string beneath the bend in the bent sub is straight, the torque exerted by the drill bit is proportional to, amongst other factors, the angle through which the bent sub is bent, and the distance between the drill bit and the bend of the bent sub. These torsional stresses may be compounded. if the drill bit is misaligned relative to the lower portion of the bent sub.
Further, some orienters cannot rotate while there is weight-on-bit, either because of the operation of their actuating mechanism, or because they are simply not powerful enough.
With bent subs, and with most orienters, there is only one degree of control, the azimuth of the deviation, i.e. the angle which the bent sub or orienter produces in the 360xc2x0 range as seen looking longitudinally along the drill string. The magnitude of the deviation, is the angle between the axis of the drill string and the bent sub or orienter, is fixed (at a few degrees). However, GB 2 278 137 A (Camco/Pringle and Morris) shows a down hole assembly having a bent sub with a movable joint. The movable body, which is coupled to the main housing by a universal joint, has its upper end enclosed in a bore in the end of the housing, and normally hangs freely in the straight position. A mandrel can withdraw the movable body into the housing; the movable body has an offset head end which forces it to skew relative to the housing. The movable body is keyed to the housing to prevent rotation. Thus this can achieve a certain amount of control over the magnitude of the deviation.
GB 2 271 795 A, Stirling Design/Head shows an orienter which provides azimuth control. An annular piston can be moved longitudinally, and has helical engagement to convert the movement into rotation. This rotation is splined to a collar with an eccentric bore. The central tube of the assembly passes through this bore (emerging as nose tubing carrying the motor and drill bit at its end), so rotation of the collar bends the tube to the side. In the embodiments of FIGS. 8, 9 and 14, magnitude control is also provided. This is achieved by; a separate mechanism attached to the nose of the apparatus.
The main object of the present invention is to provide an improved orienter giving 2 degrees of control.
According to the invention there is provided an orienter comprising a main body couplable to a drill string, a nose tubing movably mounted in the main body, and a collar with a bore which engages in a cam-like manner with the nose tubing and movable to control the orientation of the nose tubing wherein the collar is movable longitudinally and I circumferentially to control both the angle of inclination and the azimuth of the nose tubing.
Preferably the mounting of the nose tubing is a universal joint. Preferably also the collar engages with an extension of the nose tubing on the drill string side of the universal joint. Preferably also the nose tubing is aligned on both sides of the universal joint and the bore of the collar is angled relative to the main axis of the main body.
The collar is preferably hydraulically or electrically controlled.